gh-111178: fix UBSan failures in Modules/{blake2,md5,sha1,sha2,sha3}module.c

[picnixz]

Effective commits

• fix UBSan failures in blake2module.c
• fix UBSan failures in md5module.c
• fix UBSan failures in sha1module.c
• fix UBSan failures in sha2module.c
• fix UBSan failures in sha3module.c

Cosmetics

• suppress unused return values
• remove redundant casts in constructors
• suppress unused parameters in {md5,sha*,blake2}module.c

• Issue: UBSan: Calling a function through pointer to incorrect function type is undefined behavior #111178

[encukou]

One nitpick to keep in mind for the future: C standard reserves identifiers that start with underscore and capital letter, so e.g. defining _Blake2Object_CAST is technically undefined behaviour.
(Same with _Py*, of course. It'd be nicer to not add new ones in addition to _Py.)

[picnixz]

Oh... I was not aware of this. All my branches use an underscore so that the macro is really thought as being private. I can update the PRs locally as they are not yet pushed if you think it's something we should do.